1. Field of the Invention
This invention relates broadly to measuring instruments. More particularly, this invention relates to highly accurate measuring instruments having diamond coated contacts and to a method of applying the diamond coating to the contacts.
2. State of the Art
As the science of metrology becomes more precise and exacting, the need for dependable and consistent measuring instruments has become essential. Measuring instruments such as micrometers and calipers have highly parallel contact surfaces which may be subject to considerable wear, particularly if they are used to measure highly abrasive materials, such as sandpaper, grinding wheels, etc. Such wear may cause irregularities on the contact surfaces which decalibrate the instrument and yield incorrect and inconsistent measurements. Thus, where the precision of a measurement is crucial, it may be necessary to recondition the contact surfaces to make them smooth and parallel and to recalibrate the measuring instrument. Such a procedure, however, in addition to being costly, removes the instrument from use for the period of time necessary to machine it and to recalibrate it. Although the irregularities in the contacts of a measuring instrument may be too small to be noticed by a user, who may then fail to recalibrate the instrument, these irregularities may still significantly affect the precision of its measurements, and cause finished parts to be measured inaccurately.
In order to minimize the wear on the above discussed measuring instrument contacts, it is known in the art to provide a layer of hard material, such as tungsten carbide, at the contact surfaces. Tungsten carbide, however, is still subject to frequent wear and decalibration when the instrument is used to measure abrasive materials which are harder than tungsten carbide and/or chemically active with its cobalt binder. It is therefore desirable to use a harder, chemically inert, and more wear resistant material as a contact surface. The hardest known material is diamond. The hardness of diamond combined with its low coefficient of friction would make it ideal for use as a contact surface in measuring instruments. However, there is no apparent way to apply a diamond surface to the contacts of a measuring instrument. While it might be possible to braze diamond pads to the contact surfaces of a micrometer, this would present several significant problems. First, the contact surfaces of a micrometer must be perpendicular to the shaft, and parallel to each other, within ten one-millionths of an inch at every point. This would require the diamond pads to be almost perfectly parallel relative to each other and perpendicular relative to the shaft. The hardness of diamond makes it difficult to cut and grind to this required accuracy. Also, the cost of a diamond pad is prohibitive because the pad must be fabricated from a larger diamond and machined at great expense to this required tolerance of parallel sides.